In pharmaceutical and medical fields, various plugs for medical purposes are used. Hereinafter, the technology concerning such plugs for medical purposes will be described with a pre-filled syringe in which such a plug for medical purposes takes a particularly important functional role, as an example.
Recently, a so-called pre-filled syringe has become frequently used. In the pre-filled syringe, a syringe barrel serving both as an injection cylinder and a drug liquid container is preliminarily filled with a drug liquid, and the syringe barrel is transported and stored in the condition that a tip end part to which a needle is to be attached is hermetically sealed with a top cap, and before administration of the drug liquid, a needle is attached to the tip end part of the syringe barrel from which the top cap has been removed, and then a piston rod (pushing rod) is pushed-in to slide the gasket toward the tip end of the syringe barrel, and thus the drug liquid in the syringe barrel is administered.
The pre-filled syringe is featured by the ability to administer a correct dose of a drug liquid without erroneous use of the drug liquid, non-necessity of a drug liquid transferring operation, and the ability to prevent microbial contamination of a drug liquid caused by the transferring operation.
In conventional pre-filled syringes made of resin, the gasket is made of vulcanized rubber or the like. For ameliorating the “poor sliding properties” when the rubber gasket slides on the inner surface of the syringe barrel, it is necessary to apply silicon grease on the surface of the gasket or on the inner surface of the syringe barrel, and decrease in titer due to adsorption of an active ingredient in the drug liquid by the silicon grease, and contamination of the drug liquid by silicon microparticles in the silicon grease and adverse effect thereof on a human body have been seen as problems. Also, there is a “problem with regard to a liquid contact surface” because a soluble ingredient in the rubber can elute into the drug liquid.
For solving these problems, a gasket in which a covering film formed of a polytetrafluoroethylene (hereinafter, also referred to as “PTFE”) film is overlaid on the surface of a rubber gasket body has been developed. In such a gasket, the covering film formed of a PTFE film allows improvement in sliding properties of the gasket relative to the syringe barrel, and the like without use of silicon grease.
Here, as a method for producing a PTFE film which is to be a covering film, the following two methods are known: (1) following thermal pressure bonding of a laminate of at least two skived films obtained by cutting (skiving) a PTFE pressure-molded product, a thermal fusion treatment is conducted at a temperature higher than or equal to the melting point of PTFE to form a film (e.g., see Patent Literature 1), and (2) using a suspension containing PTFE resin powder, a dispersing agent, and a solvent as a material, a PTFE cast film having a center line mean roughness Ra of surface of 0.05 μm or less and a coefficient of kinetic friction of 0.2 or less is produced by a casting method (e.g., see Patent Literature 2).
By covering the surface of a gasket body with a covering film formed of a PTFE film produced by the foregoing methods, it is possible to improve the sliding properties of the gasket relative to the syringe barrel as described above, and to eliminate the need of applying silicon grease on the inner surface of the syringe barrel, thereby avoiding the aforementioned problems caused by the silicon grease.
Further, since the covering film is configured to be substantially water vapor impermeable by eliminating almost all of fine pinholes and fusion defective parts, it is possible to prevent a rubber ingredient (soluble ingredient) of the gasket body from leaching into the drug to contaminate the drug liquid. Therefore, the covering film can exert the aforementioned effect by being overlaid not only on the gasket for syringe where sliding properties are regarded as the most important properties, but also on a liquid contact inner surface of an insertion bore of a top cap for syringe into which a tip end part of the syringe barrel is to be inserted, or on a liquid contact surface of an insertion portion of a laminate rubber plug for vial, for its water vapor impermeability and barrier properties against a leached ingredient as described above.